Phenomenon flow induced phase

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

Flow Induced Phase Inversion Phenomenon and PI in Particle Technology... 

Akay, G. Dogru, M. Calkan, B. Calkan, O.F. Flow induced phase inversion phenomenon in process intensification and micro-reactor technology. Process intensification in water-in-crude oil emulsion separation by simultaneous application of electric field and polymeric demulsifiers. In Microreact Technology and Process Intensification Wang, Y., Halladay, J., Eds. Oxford University Press Oxford, 2005 Chapter, 18. 

In this study, after a brief introduction to PI we provide the bases of a technique for the preparation of polymeric micro-porous materials, known as polyHIPE polymers (PHPs) which are now used extensively in PIM, and micro-reactor technology. These polymers are prepared through the high internal phase emulsion (HIPE) polymerization route. In order to control the pore size, the flow-induced phase inversion phenomenon is applied to the emulsification technique. The metalization of these polymers and formation of nano-structured micro-porous metals for intensified catalysis are also discussed. Finally, we illustrate the applications of these materials in chemical- and bioprocess intensifications and tissue engineering while examining the existence of several size-dependent phenomena. 

Flow-Induced Phase Inversion (FIPI) Phenomenon... 

Flow-induced phase inversion (FIPI) phenomenon was observed by Akay[ and used extensively in phenomenon-based PI, especially in particlet and emulsion technologies po.21,27-32] pjpj readily observed in multi-phase systems and most... 

When disperse phase of the coarse emulsion wets the membrane wall and suitable surfactants are dissolved in both liquid phases, the process results in a phase inversion namely a coarse OAV emulsion is inverted into a fine W/O emulsion (Figure 6.1c), and vice versa (Suzuki et al, 1999). The main advantage of this method is that a fine emulsion can be easily prepared from a low concentration coarse emulsion at high rates. For polytetrafluoroethylene (PTFE) membrane filters with a mean pore size of 1 im, the maximum dispersed phase volume fraction in phase-inverted emulsions was 0.9 and 0.84 for O/W and W/O emulsions, respectively (Suzuki et al., 1999). Flow-induced phase-inversion (FIPI) phenomenon was observed earlier by Akay (1998) who used a multiple expansion-contraction static mixer (MECSM) consisting of a series of short capillaries with flow dividers. Hino et al. (2000) and Kawashima et al. (1991) inverted a W/O/W emulsion made up of liquid paraffin. Span 80 (a hydrophobic surfactant), and Tween 20 (a hydrophilic surfactant) into a W/ O emulsion by extrusion through polycarbonate membranes with a mean pore sizes of 3 and 8 im. Inside the membrane pores, surfactant molecules are oriented with their hydrophobic groups toward the wall surface and with hydro-phihc groups toward the solubilized water molecules as a result of a lamellar structure formed inside the pores. The structure ruptured at the pore outlets. 

The effects of flow rate (flow intensity, turbulence, shear stress) on corrosion have been known for a long time and have been variously called erosion corrosion or flow induced localized corrosion (FILC), which latter term is preferred because it denotes a purely aqueous (liquid) phenomenon, while erosion generally includes the presence of a solid phase. An attempt was made in 1990 to summarize the state of the art of FILC in a symposium [54]. The following is a brief synopsis of the developments in this area, with emphasis on corrosion inhibitor testing. 

With the flowing mobile phase another phenomenon is observed. Those molecules that are in touch with the solid material move more slowly, while the others, passing through the center of the pores, displace more quickly. This friction-induced inequality of the flow rates additionally contributes to broadening of a chromatographic spot. 

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

Flow movement also has a relationship with the electrokinetic phenomenon, which can promote or retard the motion of the fluid constituents. Electrokinetic effects can be described as when an electrical double layer exists at an interface between a mobile phase and a stationary phase. A relative movement of the two phases can be induced by applying an electric field and, conversely, an induced relative movement of the two will give rise to a measurable potential difference.33... 

Solvent effects may in certain cases contribute to the charge conduction mechanism with polymer films, however, as the work of Kaufman et al (24) has shown. On the basis of spectral data, these workers have concluded that mixed valence states of tetrathiafulvalene (TTp2+, TTF" ", etc.) are not essential to charge-conduction in poly TTF films, but that electron hopping modulated by the solvent-induced pendent group collisions is. An additional phenomenon related to the electrolyte noted by this group is that ion flow into the polymer phase appeared to limit the kinetics of oxidation reactions in these films. 

Hetsroni et al. [3] also found evidence of a coupling phenomenon for an array of 17 parallel microchannels. In Fig. 7 from [3], they found evidence of two-phase flow oscillations. Only one channel is followed as a function of time. The water-steam flow is from the left to the right. Steam appears in the 5th picture. The liquid-vapor interface then moves to the exit or to the entrance. This interface movement is representative of a non-constant mass flow provided to the microchannel. The inlet condition before the plenum is a constant inlet pressure however, due to the plenum, the flow can come back and induce such coupling. The frequency of the interface oscillation can usually be related to the total pressure drop oscillation frequency. 

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